Electrodeposition of fine-grained lustrous nickel



United States Patent- O 3,152,971 ELECTRGDEPOSITION F FINE-GED LUSTRQUSNICKEL Thaddeus W. Tornaszewski, Dearborn, and Henry Brown,

Huntington Woods, Mich, assignors, by mesne assignments, to The UdyliteCorporation, Warren, Mich, a corporation of Delaware N0 Drawing. Filed.luly 26, 1960, Ser. No. 45,285

' 22 Claims. (Cl. 204-41) This invention relates to theelectrodeposition of nickel with a satin-like appearance directly fromaqueous acidic nickel baths. More particularly this invention provides amethod for obtaining a fine-grained lustrous satin nickel plate ofexceptional corrosion resistance directly from the plating bath.

, Satin or brushed finished nickel or chromium plate is normally moreexpensive than the bright nickel finishes which are obtained withhigh-leveling, bright nickel plating which require no further polishingor bufling. To obtain the most pleasing satin finishes, dull nickel ordull chromium plate is most often employed, and is subsequently brushfinished to obtain the satin lustre. This latter step is expensive, andalso decreases the corrosion protection afforded by'the satin platebecause the brush marks or polishing scratches penetrate appreciably inthe plate especially in recessed areas where the plate is thin. Forthese reasons, that is, expense, and decreased corrosion resistance,satin finished nickel or chromium are not usually used for exteriorparts of automobiles or boats.

It is an object of this invention to provide plating baths and methodsto produce fine-grained lustrous satin nickel directly from the baththat not only has a very pleasing appearance, but which can behigh-lighted by bufiing raised area to give beautiful two-tone efiects,and which will also provide exceptionally good corrosion protection tothe basis metal such as ferrous, aluminum, magnesium, brass, copper andzinc articles.

It has now been found that nickel plating baths normally designated asbright nickel baths, or semi-bright nickel baths can be modified toplate a fine-grained lustrons satin nickel deposit, by incorporating inthese baths certain quantities or concentrations of certain finelydivided bath insoluble compounds, and plating while these powderedmaterials are maintained in agitation in these baths. The method of theinvention also includes the step of removing from the plated surface anyexcess powdery material clinging to the plate prior to additionaltreating steps, such as the preferred final step of chromium platmg.

The bath insoluble fine powders which when added to agitated brightnickel or semibright nickel plating baths in concentrations from to 500grams per liter produce a pleasing fine-grained lustrous satin nickeldirectly from the bath, are certain oxides, carbides, silicides,nitrides, fluorides and sulfides of the group consisting of siliconcarbide, boron carbide, titanium carbide, silicon dioxide, manganeseoxide, titanium oxide, zirconium oxide, aluminum oxide, ceric oxide,ferric oxide, chromic oxide, boron nitride, calcium fluoride, strontiumfluoride, barium fluoride, stronium fluoride, barium fluoride, zincsulfide, cadmium sulfide, and iron silicide.

It is thought that these materials function in a similar manner toproduce the satin plate of this invention because they all have thecommon property of being semi- 3,152,971 Patented Oct. 13, 1964 "iceconductors and are either bath insoluble or do not decompose in the bathto release components, during electrodeposition or upon standing, whichdetrimentally aifect the plating characteristics of the bath.

These materials must be used in the form of very fine powders withaverage diameters of less than about 2 microns, otherwise roughness ofplate occurs especially on shelf areas of articles where the particlescan settle.

The preferred particle size is from about 0.02 to 0.5 micron averagediameter, and when used in concentrations of about 10 to 200 grams perliter in agitated bright or semi-bright nickel plating baths produce asmooth fine-grained lustrous satin nickel deposit. The surface of thesatin nickel plate obtained under these conditions has approximately 20million micro-pits per sq. in. as determined by microscopic evaluationat 250x magnification. If the powders are from 0.02 to 0.05 micronultra-fine particle size, concentrations can be used of about 10 toabout grams per liter. If the particle size is about 0.1 to 0.4 micron,then concentrations of about 50 to 200 grams per liter give the bestresults.

Especially desirable results from a decorative as well as a corrosionresistant standpoint are obtained by the addition of these very finepowders, in concentrations of about 50 to 200 grams per liter toair-agitated bright nickel plating baths such as those described in U.S.2,647

866, issued August 4, 1953; 2,800,440 and 2,800,442, issued July 23,1957. Superfine powders of 0.02 to 0.5 micron particle size areespecially outstanding in preformance. The nickel plate obtained fromthese agitated bright plating baths containing, for example, about75-200 grams per liter of these superfine powders, has a semibrightmicroscopically-fine pitted surface with a satin smooth sheen of verypleasing appearance. The fine suspended powders tend to cling to thenickel plate, and this eiiect and the specific physical structure,particle size and shape, and the chemical structure of the powderapparently causes the microscopically-fine pitting effect which convertsthe normally bright or semi-bright surface to a satin smooth sheen. Theuniformity of the sheen is unusual and especially noteworthy in that a0.2 mil to 2 mil thick or thicker plate can have the same satinappearance. Thus, when contoured articles such as camera parts,ornaments, grilles, automobile dashboards, door handles, marinehardware, etc., are plated, the satin appearance of the plate in therecessed areas (low current density areas) is the same as the plate inthe higher current density areas.

Concentrations of the fine powders as high as 500 grams per liter in thebath do not produce any appreciably difierent results than the optimumconcentrations of about 50 to 200 grams per liter. Air agitation ormechanical agitation including ultra-sonic agitation of the baths can beused. The faster or more powerful the agitation and the finer theparticle size down to colloidal dimensions, the lower the concentrationof fine powder that is necessary, and concentrations as low as 10 gramsper liter may be used to obtain a smoky satin finish by using strongagitation and powders having a size of about 0.1 to 0.3 micron orultra-fine particles having a size of 0.02 to 0.04 micron. Agitation isnecessary to keep the fine powder suspended in the bath during plating.In general, however, it is preferred to use from about 50 to 200 gramsper liter of very fine powder having a size less than 2 microns inair-agitated baths.

Analysis of a satin nickel plate from an air agitated bright nickel bathcontaining these superfine insoluble powders of particle size of 0.02 to0.5 micron in a concentration of about 100400 grams per liter showsusually not higher than about 2.4% to 2.5% insoluble powder uniformlydistributed in the nickel plate. Microscopic examination of the surfaceof the plate shows an extremely uniform finely pitted surface. Thissatin plate has excellent adhesion, for example, to ferrous, copper, andbrass surfaces just as the plate from the clear nickel bath, and it isquite surprising that these agitated baths containing 100 to 200 gramsper liter of these superfine powders give exceptionally smooth to thetouch satin plate even in 20 mil and thicker plates, and thatpractically no gas pitting occurs. The addition of these fine powders inthe same concentrations, that is, 50 to 200 grams per liter to agitatedplain dull nickel baths, such as the Watts bath, makes the dull nickelplate obtained even duller and more unsightly in appearance.

The throwing power and covering power of the agitated bright nickelbaths with the suspended powders is about the same as without the finepowders present. It

, was found that in plating articles with recessed areas and with shelfareas that no roughness was obtained on the areas on which settling canoccur.

The leveling of the bright nickel plate is' not decreased by thepresence of these fine insoluble powders in the bath. In fact, theleveling seems definitely improved in most cases.

The satin nickel plate obtained from bright or semibright nickel platingbaths containing these fine powders can easily be polished or bulfed toa high lustre, thus, as already mentioned beautiful two-tone effects canreadily be obtained by buffing raised or accessible portions of thesatin nickel plated object. Also, where a brush satin finish is desired,this can be accomplished by using, for example, 120 or 150 emery polishon the basis metal, then these coarse polishing lines can be seen in thesatin sheen nickel, despite the bi h leveling characteristics of thebaths. That is, the coarse polishing lines are only partially smoothenedout. Thus, in this way, an excellent brush type satin finish is obtainedof higher corrosion protection than when a nickel plate is brushed afterplating.

When concentrations of less than about grams per liter of the ultra-finepowders are used in agitated bright or semi-bright nickel plating baths,then the satin appearance of the nickel plate decreases, and the platehas a smoky appearance and has more reflectivity, especially in recessedareas. Thus, it is preferred for the most general satin finishapplications as well as corrosion protection applications to useconcentrations of the very fine powders greater than about 10 grams perliter.

The use of dispersing agents, peptizing agents in conjunction with thefine powders is often helpful, though not necessary. There are notparticular operating troubles because concentrations of 150 grams perliter or higher of these fine powders are used in the bath instead of,for example, 40 to 50 grams per liter of 0.02 to 0.5 micron particlesize. The powders of extremely fine or ultra fine particle size of 0.02to 0.04 micron or less, are generally more expensive, that is, if thegreat percentage of the particles are of these ultra-fine diameters,however, lower concentraiton can be used to obtain equivalent elfects.Before technical grade powders are used commercially they should alwaysbe checked first in small scale tests such as 1-4 liter baths beforebeing added to large baths because certain harmful impurities such asmetallic powders or too coarse particles may be present which will causerough plate, especially on shelf areas. Except for the necessity of thisprecautionary check, technical grade powders normally produce equalresults to those obtained from the use of high purity grades of the sameparticle size and structiu'e. Also, if the powder is not wetted properlyby the nickel bath, it should be checked for freedom of fatty or oilyfilms.

i 1 It is important to avoid metallic powders in these baths, forexample, poorly cast nickel anodes which might powder during use anddisperse nickel particles in the bath definitely can cause roughness,also high concentrations of activated carbon in the bath can cause veryundesirably roughness. The carbon from rolled or cast carboncontainingnickel anodes, however, does not usually cause roughness when floatingin the baths. High concentrations of iron dissolved as ferrous or ferriciron in the baths do not cause settling roughness or gross pittingeffects in the baths even at the pH values of 3.8 to 5.5 although atsuch pH values dissolved iron tends to precipitate. Zinc or cadmium ionscan be present in the baths in concentrations as high as about one gramper liter without detrimentally affecting the plate. Cadmium tends towhiten the plate somewhat. The presence of sodium and magnesium saltsare not harmful. Ammonium salts in' concentrations higher than about 15grams per liter is in general not desirable because of reduction of thelimiting cathode current density. In general, bright or semi-brightnickel plating baths of the Watts, high chloride, sulfarnate andfiuoborate baths or mixtures can be used. Also, other buffers besidesboric acid may be used, such as formates, citrates, etc.

The pH of the baths may be from about 2 to 6, though the preferred pHvalues are from about 3.5 to 5.2. The temperature of the baths can befrom room to at least 170 F., though in general a temperature of aboutF. to about F. is preferred.

As already mentioned, the use of these fine insoluble powders does notcreate a satin sheen nickel plate when added to plain nickel baths thatnormally produce dull nickel deposits such as the Watts nickel bath. Thenickel bath must be a semi-bright or bright nickel plating bath. Thebest addition agents or brighteners to achieve the semi-bright andbright nickel plating conditions necessary to obtain satin nickel afterthe addition to the bath of the aforementioned powders in concentrationsof about 10 to 500 grams per liter are the following: the brighteners ofthe class of organic Salton-compounds including aromatic and unsaturatedaliphatic sulfonic acids, sulfonamides .and sulfonimides, such asbenzene sulfonic acids, naphthalene sulfonic acids, p-toluenesulfonamide, benzene sulfonamide, o-benzoyl sulfimide, allyl sulfonicacid, 2-butyne-1,4-disulfonic acid, o-sulfobenzaldehyde, etc.; theaddition agents which produce semi-bright sulfur-free nickel plate suchas formaldehyde, chloral hydrate, bromal hydrate, cournarin, butynediol, used alone or in combinations; combinations of the sulfur-freeaddition agents with those of the organic sulfon-type, and combinationsof the latter with small concentrations of amines, such as quinaldine orunsaturated compounds such as N-allyl isoquinolinum bromide and otherunsaturated compounds, polyamines, etc. I

Cobalt and iron can be present in the nickel bath as the cobalt orferrous sulfates, chlorides, sulfamates or fluoborates in concentrationsas high as at least 40 grams per liter, yielding nickel alloy platescontaining concentrations of cobalt and/ or iron as high as at least50%.

Surface active agents may be present in the baths, but are not usuallynecessary in the air agitated baths.

The maximum increase in satin sheen is obtained when the fine powdersare used in the agitated full bright nickel plating baths such as theair-agitated bright nickel plating baths possessing good leveling asthose illustrated in Examples 1, 2 below. Less satin lustre, for examplethat of Example 3, is obtained when the nickel baths contain only thecarrier type brightener such as benzene sulfonic acids, naphthalenesulfonic acids, p-toluene sulfonamide, benzene sulfonamide, o-benzoylsulfimide, etc. In the latter cases the satin lustre is flatter. This isalso true when the semi-bright sulfur-free type of addition agent suchas formaldehyde, chloral hydrate, or bromal,

is used solely with the fine powders, and with these sulfur-freesemi-bright addition agents such as those mentioned, as well ascoumarin, it is best to use the ultra-fine particle size powders of lessthan 0.2 micron particle size, and preferably less than 0.05 micronparticle size as determined with the electron microscope. There seems tobe a definite improvement in leveling with the semi-bright sulfur-freeaddition agents when these ultra-fine particle size powders are used.The corrosion protection to steel, aluminum, magnesium, and zinc basedie-castings of such chromium plated nickel is greatly improved as shownby repeated passage of such severe accelerated tests as the Corrodkote,with and without a final, sulfur-containing bright nickel overlay plateto give a double layered plate, so-called duplex or dual nickel, of 40to 60 ratio to 80 to 20 ratio of ultra-fine satin semi-brightsulfur-free nickel to fully bright nickel. Furthermore, it was foundthat the satin nickel plate obtained from the agitated bright nickelplating baths containing organic sulfontype addition agents and the finepowders as illustrated in Examples 1, 2 and 3 when plated to a thicknessof 1 to 1.5 mils on steel or copper plated zinc die-cast and given theusual 0.01 mil final chromium will itself pass many successiveCorrodkote and Cass tests of 20 hours each without any failure. This isdue mainly to the development of a very fine favorable porosity patternin the final thin, 0.01 mil, chromium plate. If the fine powders of thisinvention are omitted, the resulting full bright nickel plate'of thesame thickness and with the same thin final chromium plate will fail inonly one cycle of 20 hours Corrodkote testing.

There is a strong tendency for the finely-divided powders to remainclinging to the nickel surface after the plated article is withdrawnfrom the bath and rinsed thoroughly. They often remain clinging evenafter the usual final chromium plate of 0.005 to 0.05 mil is applied.For such clinging particles which are only slowly soluble in acids orsequestering agents, it was found that a very thin plate from a zinccyanide bath (about 1 to 3 minutes plating) followed by an acidic oralkaline dip to remove the zinc, also removed the tightly clingingparticles. Actually, the particles on the work look like a fine dust andare not really too unsightly even if left on, and they do not hurt thechromium plate. They are readily wiped oil with a cloth, or, they can beremoved to a certain extent by ultrasonic cleaning.

The satin nickel plate accepts chromium plate like regular nickel plate,and in general only the usual thicknesses of final chromium need beused, that is, 0.01 mil, though thicknesses of 0.1 mil or 0.2 mil may beused. Besides, the final satin nickel finish as such, or with the usualfinal chromium finish, the satin nickel plate can be given a rhodium,silver, tin, brass, bronze, copper, gold, or tinnickel (65-35) alloy orother final thin coating. Thin wax, or soluble-wax, films or clearlacquers greatly decrease finger marking of the final coatings, such asnickel, bronze, silver, brass, etc. Chromium, gold, rhodium, andtin-nickel alloy plate do not need these organic coatings.

In general, for indoor use, satin nickel coatings of only 0.2 to 0.5 milthickness are needed. For outdoor exposure in industrial or marineatmospheres thicknesses of 1 to 1.5 mils should be used. Also, the satinnickel can be used as the top layer of a double layered or duplex nickelcoating, with the undercoat consisting of at least 0.7 mil ofsemi-bright sulfur-free nickel. This would be for the most severeoutdoor exposure as for marine hardware. As already mentioned, however,the corrosion protection to steel, aluminum, magnesium, brass and zincof the satin nickel with the usual final chromium plate (0.01 mil) evenfrom baths containing organic sulfon-compounds is amazingly superior tothe fully bright nickel obtained from the same baths without the finepowders present.

' Below are listed some preferred examples of baths forby Examples 1 to5. In general, the cathode current density is from 10 to amps/sq. ft.Mixtures of powders may be used, such as zirconium'oxide with titaniumoxide, aluminum oxide with nickel carbonate, barium fluoride withtitanium oxide, .etc. It is important that the powders are clean andwetted by the aqueous nickel bath.

Example I Conc., grams/liter Zirconium oxide fine powder (0.03 to 0.3micron particle size) 40-150 NiSO 6H O 15 0-300 NiCl 6H O 30-100 H 8030-40 p-Toluene sulfonamide 1-2 o-Benzoylsulfimide 0.1-2 Allyl sulfonicacid 0.5-6 N-allyl quinaldinium bromide 0.002-0.01

pH=3.0-5.2. Temp.=room to F. Air agitation of the bath.

Example II Cone, grams/liter Titanium oxide superfine powder (0.03 to0.5

micron) 30-200 NiSO -6H O 150-300 NiCl -6H O 30-150 H BO 30-40 o-Benzoylsulfimide 1-3 Allyl sulfonic acid 0.5-4 2-butyne-l,4-disulfonic acid0.1-10 2-butynoxy-1,4-diethane disulfonic acid 0.05-0.1

pH=2.S to 5.2. Temp.=room to F. Air agitation or mechanical agitation.

Example III Conc. grams/ liter Titanium oxide superfine powder 30-200NiSO -6H O 75-200 NiCl -6H O 30-150 H3BO3 30-40 o-Benzoyl sulfimide 1-3p-Toluene sulfonamide l-2 pH=3.0 to 5.0. Temp.=room to F. Air agitationor mechanical or both.

Example IV Conc. grams/liter Zirconium oxide ultra-fine powder,0.02-0.04

Temp.=room to 150 F. Mechanical or air agitation or both.

Example V Conc. grams/liter Aluminum oxide superfine optical powder10-200 NiSO -6H O 100-300 NiCl 6H O 30-75 H 30 30-40 Allyl sulfonic acid1-3 Benzene sulfonamide 1-3 2-butynoxy-L4-diethane disulfonic acidpH='5.0-5.2.

Temp.=room to 160 F.

Air or mechanical agitation.

2' Example VI Conc. grams liter pH=5.0 to 5 .2 Temp.=r0om to 150 F.Mechanical agitation.

The satin nickel plate of this invention has about 10 million to about50 million micro-pits per square inch, as determined by microscopicevaluation at 250 Xmagnification, and in all cases the plate contains asufficient number of micro-pits to give the plate a microscopic satinappearance.

What is claimed is:

1. A method for electrodepositing a fine-grained lustrous plate which isessentially nickel comprising the step of electrolyzing an aqueousacidic solution of at least one nickel salt selected from the groupconsisting of nickel sulfate, nickel chloride, nickel fluoborate, nickelsulfamate and mixtures of at least one said nickel salt with up to about40 grams per liter of at least one salt selected from the groupconsisting of the sulfates, chlorides, fluoborates and sulfamates ofcobalt and iron and at least one soluble organic addition agent capableof producing said fine-grained lustrous plate, said bath containingdispersed therein about 10 to about 500 grams per liter of at least onematerial selected from the group consisting of silicon carbide, boroncarbide, titanium carbide, silicon dioxide, manganese oxide, titaniumoxide, zirconium oxide, aluminum oxide, ceric oxide, ferric oxide,chromic oxide, boron nitride, calcium fluoride, strontium fluoride,barium fluoride, zinc sulfide, cadmium sulfide and iron silicide, saidmaterial in said bath being in the form of a fine powder, the size ofwhich is less than about 2 microns average diameter, continuing saidelectrolysis until an adherent decorative nickel plate is formed on saidsurface, and thereafter electrodepositing thereon an 0 erlayer of ametal selected from the group consisting of chromium, rhodium, silver,tin, brass, bronze, copper, gold and an alloy consisting'of about 65 tinand about nickel.

2. A method for electrodepositing a fine-grained lustrons nickel platecomprising the step of electrolyzin-g an aqueous acidic solution of atleast one nickel salt and at least one soluble organic addition agentcapable of producing said fine-grained lustrous plate, said bathcontaining dispersed therein about $10 to about 500 grams per liter ofat leastone material selectedfrom the group consisting of siliconcarbide, boron carbide, titanium carbide, silicon dioxide, manganeseoxide, titanium oxide, zirconium oxide, aluminum oxide, ceric oxide,ferric oxide, 'chromic oxide, boron nitride, calcium fluoride, strontiumfluoride, barium fluoride, zinc sulfide, cadmium sulfide and ironsilicide, said material in said bath being in the form of a fine powder,the size of which is less than about 2 microns average diameter,continuing said electrolysis until an adherent decorative nickel plateis formed on said surface, and thereafter electrodepositing thereon anoverlayer of a metal selected from the group consisting of chromium,rhodium, silver, tin, brass, bronze, copper, gold and an alloyconsisting of about 65% tin and about 35% nickel.

3. A method in accordance with claim 2 wherein said fine powder iszirconium oxide.

4. A method in accordance with claim 2 wherein said fine powder istitanium oxide.

5. Amethod in accordance'with claim 2 wherein said fine powder issuperfine aluminum oxide optical powder.

6. A method in accordance with claim 2 wherein said fine powder iscalcium fluoride.

7. A method for electrodepositing a fine-grained lustrous nickel platecomprising the step of electrolyzing an aqueous acidic solution of atleast one nickel salt selected from the group consisting of nickelsulfate, nickel chloride, nickel fluoborate, and nickel sulfamate and atleast one soluble organic addition agent capable of producing saidfine-grained lustrous plate, said bath containing dispersed thereinabout 10 to about 500 grams per liter of at least one material selectedfrom the group consisting of silicon carbide, boron carbide, titaniumcarbide, s licon dioxide, manganese oxide, titanium oxide, zirconiumoxide, aluminum oxide, ceric oxide, ferric oxide, chromic oxide, boronnitride, calcium fluoride, strontium fluoride, barium fluoride, zincsulfide, cadmium sulfide and iron silicide, said material in said bathbeing in the form of a fine powder, the size of which is less than about2 microns average diameter, and thereafter plating on said cleanedsurface an overlayer of a metal selected from the group consisting ofchromium, rhodium, silver, tin, brass, bronze, copper, gold, and analloy consisting of about 65% tin and about 35% nickel.

8. A method in accordance with claim 2 wherein the metal of saidoverlayer is chromium.

9. A method in accordance with claim 2, wherein said fine powder isessentially silicon dioxide, and an average diameter of the individualparticles thereof is less than about two microns.

10. A composite electroplate on a metal surface susceptible toatmospheric corrosion which comprises a nickel plate with a metallicover-lay, said nickel plate having been electrodeposited from an acidicnickel plating bath containing dissolved therein at least one organicnickel brightener capable of producing semi-bright to fully brightnickel plate, and having dispersed in said bath at least one type ofbath insoluble inorganic non-metallic particles the average diameter ofthe individual particles thereof being less than about 2 microns, anelectrodeposited over-lay plate of a metal selected from the groupconsisting of chromium, rhodium, silver, tin, brass, bronze, copper,gold and an alloy consisting of about 65% tin and about 35 nickel onsaid nickel plate said over-lay plate being less than about 5 microns inthickness, said type of particles in said nickel bath being selectedfrom the group consisting of silicon carbide, boron carbide, titaniumcarbide, silicon dioxide, manganese oxide, titanium oxide, zirconiumoxide,'aluminum oxide, ceric oxide, ferric oxide, chromic oxide, boronnitride, calcium fluoride, strontium fluoride, barium fluoride, zincsulfide, cadmium sulfide and iron silicide, and said fine particlesbeing present in said nickel bath in an amount sufficient to produce afine porosity pattern in the said over-lay plate.

11. A composite electroplate in accordance with claim 10, wherein saidnickel plate directly overlies an electrodeposit consisting essentiallyof nickel.

12. A composite electroplate in accordance with claim 10 wherein saiddissolved organic nickel brightener is selected from the groupconsisting of aromatic and unsaturated aliphatic sulfonic acids,sulfonamides and sulfonimides.

13. A composite electroplate in accordance with claim 10 wherein saidbath insoluble inorganic non-metallic particles are present in thenickel bath in a concentration of at least about 10 grams per liter.

14. A composite electroplate in accordance with claim 12 wherein saiddissolved organic nickel brightener is obenzoyl sulfimide.

. 15. A composite electroplate in accordance with claim 10 wherein saidover-lay plate is chromium.

16. A composite electroplate in accordance with claim 10 wherein saidnickel plate directly overlies an electrod eposit consisting essentiallyof lustrous nickel.

17. A composite electroplate in accordance with claim 10 wherein saidnickel plate directly overlies an electrodeposit consisting essentiallyof lustrous nickel and said over-lay plate is chromium.

'18. A method in accordance with claim 2 wherein said overlayer ischromium.

19. A method in accordance with-claim '1 wherein said material isdispersed in said bath during plating by air agitation.

20. A method in accordance with claim 2 wherein said material isdispersed in said bath during plating by air agitation.

21. A method in accordance with claim 1 said overlayer is chromium.

22. A method in accordance with claim 1 wherein there is present in saidsolution at least one compound selected from the group consisting of=boric acid, formates and citrates.

wherein References Cited in the file of this patent UNITED STATESPATENTS

1. A METHOD FOR ELECTRODEPOSITING A FINE-GRAINED LUSTROUS PLATE WHICH ISESSENTIALLY NICKEL COMPRISING STEP OF ELECTROLYZING AN AQUEOUS ACIDICSOLUTION OF AT LEAST ONE NICKEL SALT SELECTED FROM THE GROUP CONSISTINGOF NICKEL SULFATE, NICKEL CHLORIDE, NICKEL FLUOBORATE, NICKEL SULFAMATEAND MIXTURES OF AT LEAST ONE SAID NICKEL SALT WITH UP TO ABOUT 40 GRAMSPER LITER OF AT LEAST ONE SALT SELECTED FROM THE GROUP CONSISTING OF THESULFATES, CHLORIDES, FLUOBORATES AND SULFAMATES OF COBALT AND IRON ANDAT LEAST ONE SOLUBLE ORGANIC ADDITION AGENT CAPABLE OF PRODUCING SAIDFINE-GRAINED LUSTROUS PLATE, SAID BATH CONTAINING DISPERSED THEREINABOUT 10 TO ABOUT 500 GRAMS PER LITER OF AT LEAST ONE MATERIAL SELECTEDFROM THE GROUP CONSISTING OF SILICON CARBIDE, BORON CARBIDE, TITANIUMCARBIDE, SILICON DIOXIDE, MANGANESE OXIDE, TITANIUM OXIDE, ZIRCONIUMOXIDE, ALUMINUM OXIDE, CERIC OXIDE,FERRIC OXIDE, CHROMIC OXIDE, BORONNITRIDE, CALCIUM FLUORIDE,STRONTIUM FLUORIDE, BARIUM FLUORIDE, ZINCSULFIDE, CADMIUM SULFIDE AND IRON SILICIDE, SAID MATERIAL IN SAID BATHBEING IN THE FORM OF A FINE POWDER, THE SIZE OF WHICH IS LESS THAN ABOUT2 MICRONS AVERAGE DIAMETER, CONTINUING SAID ELECTROLYSIS UNTIL ANADHERENT DECORATIVE NICKEL PLATE IS FORMED ON SAID SURFACE, ANDTHEREAFTER ELECTRODEPOSITING THEREON AN OVERLAYER OF A METAL SELECTEDFROM THE GROUP CONSISTING OF CHROMIUM, RHODIUM, SILVER, TIN, BRASS,BRONZE, COPPER, GOLD AND AN ALLOY CONSISTING OF ABOUT 65% TIN AND ABOUT35% NICKEL.